1. Field of the Invention
The present invention relates to a plastic lever, such as a tensioner lever or a guide lever, for use in a power transmission device including an endless chain trained around a driving sprocket and a driven sprocket, or a similar power transmission device including an endless belt trained around a driving pulley and a driven pulley.
2. Description of the Related Art
Conventionally, a tensioner lever and a guide lever are known as a lever used in a power transmission device having a chain or a belt (toothed belt, for example). Examples of such known lever are disclosed in Japanese Utility Model Registration No. 2519476 and Japanese Utility Model Publication No. (Hei) 7-36201. In general, the tensioner lever, in use, is in slide contact with the chain (or the belt) to apply a proper tension to the chain and also suppress vibration including lateral oscillation of the chain. The guide lever prevents undue stretch or slack of the chain (or the belt) when the chain is assembled on the driving and driven sprockets and while the chain is running around the sprockets. The guide lever also serves to prevent vibration including lateral oscillation of the chain while running.
FIG. 7 shows a conventional tensioner lever 100 composed of an arm 101 made of aluminum and a plastic shoe 102 provided on the arm 101 for sliding contact with a chain. The aluminum arm 101 has a thick longitudinal flange 101A, a mount hole 101B and a hollow portion 101C. The shoe 102 is attached to the flange 101A of the arm 101. The shoe 102 has a plurality of L-shaped side engagement strips 102A, 102B, 102C engaged with the flange 101A from one side thereof, a hook-shaped end engagement strip (not shown) engaged with a leading end of the arm 101 (when viewed from the direction of travel of the chain indicated by the arrow C), and an upright engagement strip 102E engaged with the flange 101A from the opposite side thereof. When assembling the tensioner lever 100, the plastic shoe 102 is forced over the arm 101 in a lateral direction with the upright engagement strip 102E directed forward until the L-shaped side engagement strips 102A-102C are engaged with the flange 102A on one side of the arm 101, and subsequently the upright engagement strip 102E is snap fit with a retaining recess (not shown) formed in a portion of the flange 101A on the other side of the arm 101. Reference numeral 103 shown in FIG. 7 denotes a pad adapted to be engaged with a tensioner (not shown). The conventional tensioner is pivotally mounted to a fixed member (engine body, for example) by means of a bolt (not shown) extending though the mount hole 101B. In operation, the tensioner urges the pad 103 to turn the tensioner lever 100 about the axis of the bolt in a direction to apply a proper tension to the endless chain running in the direction of the arrow C.
For attachment with the plastic shoe 102, the aluminum arm 102 of the conventional tensioner lever 100 is shaped into a complicated configuration including a flange, a mount hole and a hollow portion. Accordingly, when the arm is to be formed by casting, a casting die or mold of a complicated configuration is needed. This increases the manufacturing cost of the tensioner lever. In addition, due to the complicated configuration of the arm, the amount of metal material used is relatively large, leading to a further increase of the manufacturing cost. Alternatively when the arm is to be formed by press-working, the presence of a mount hole at an end of the arm requires cost-increasing additional precessing steps, such as rolling of a metal sheet into a tube, and insertion of a bushing into the tube. Thus, the press-formed arm is also expensive.
Furthermore, the plastic shoe 102 having various engagement strips 102A-102E of different shapes requires a molding die of a complicated configuration. In addition, the assembling process described above of the conventional tensioner 100 requires a certain care and muscular effort to secure reliable matching between the engagement strips 102A-102E and the corresponding parts of the arm 101.
With the foregoing problems in view, many attempts have been made to manufacture a lever (tensioner lever, guide lever and so on) made of a plastic. However, the prior attempts are still unsatisfactory in that due to a limited strength attained by the plastic, the plastic lever is made thick. The thick plastic lever requires a relatively large space for installation and operation. This poses a serious problem when the lever is used in an automobile engine or the like machine as a part of a power transmission device.
It is, accordingly, an object of the present invention to provide a lever assembly for a power transmission device, which is simple in construction, can be manufactured at a relatively low cost, is easy to assemble, is small in thickness but sufficient in strength, and occupies a relatively small space for installation with respect to a fixed support member such as an engine body.
To achieve the foregoing object, according to the present invention, there is provided a lever assembly for a power transmission device, which comprises a lever and a fastener for pivotally mounting the lever to a fixed support member. The lever includes a lever body made of a plastic having a mount hole extending from one surface to the opposite surface of the lever body at one end of the lever body, a central through-hole extending from the one surface to the opposite surface of the lever body at a central portion of the lever body, a first longitudinal groove formed in the one surface and extending from the central through-hole to a position in proximity to the mount hole, and a second longitudinal groove formed in the opposite surface and extending from the central through-hole to a position adjacent to the other end of the lever body. The lever also has a single reinforcement plate fitted in the first and second longitudinal grooves across the central through-hole of the lever body. The fastener extends through the mount hole and adapted to be threaded to the fixed support member so as to mount the lever pivotally to the fixed support member, the fastener having a portion lying over part of the reinforcement plate to prevent the reinforcement plate from displacing off the lever body.
The plastic lever body serves also as a shoe for sliding contact with a chain or a belt of a power transmission device. The lever body is made of a plastic, but by virtue of the reinforcement plate fitted in the first and second longitudinal grooves across the central through-hole of the lever body, the strength of the thus reinforced lever body is comparable to that of a lever made of metal.
In one preferred form of the present invention, the fastener comprises a screw having a flanged head, the flanged head lying over the part of the reinforcement plate.
In another preferred form of the present invention, the fastener comprises a flanged bushing fitted in the mount hole of the lever body and having a flange lying over the part of the reinforcement plate, and a headed screw extending through the bushing and adapted to be threaded to the fixed support member.
The reinforcement plate is assembled with the lever body by way of inserting the reinforcement plate through the central through-hole and subsequently turning the reinforcement plate about the central through-hole relative to the lever body. Thus, the reinforcement plate can be assembled with the plastic lever body with utmost ease.
It is preferable that the lever body is made of an engineering plastic, and the reinforcement plate is made of metal or fiber reinforced plastic.